1. Field of the Invention
The present invention relates generally to cables and more specifically to a voltage level conditioning transceiver cable which provides communication between RS-232 and RS-485/RS-422 serial communication ports.
2. Discussion of the Prior Art
There are several brands of programmable controllers which have RS-485/RS-422 serial communication ports. Various communications interface standards are known for establishing communications between computer systems and programmable controllers. One example of such an interface is the RS-232 serial communications interface standard which is used in many applications including IBM compatible personal computers. Interfacing a programmable controller with an RS-485/RS-422 port to a peripheral piece of equipment with an RS-232 port requires the use of an in-line device. The in-line device converts the RS-232 single ended signals to an RS-485/RS-422 differential signal. The only product commercially available to the applicant's knowledge is an adapter manufactured by Horner Electric of Indianapolis, Ind. The RS-485/RS-422 end of the Horner adapter is plugged into a programmable controller. The other end of the Horner adapter contains a 9 pin connector which is RS-232 compatible. One end of the 9-pin cable is then plugged into the RS-232 connector of the Horner adapter. The other end of the 9-pin cable is then plugged into another device such as a personal computer. If the device is a modem or an operator interface terminal, the correct 9-pin to 25-pin adapter must be used to provide the proper signal connections.
Unfortunately, the Horner adapter has some drawbacks. First, NEMA standards require that programmable controllers be contained in sealed enclosures. The straight in-line design of the Horner adapter requires the programmable controller to be placed in a sealed enclosure which is approximately 4 inches deeper than necessary. Second, the Horner adapter does not have any type of indication that communication is occurring between the programmable controller and another device. Third, the Horner controller may be damaged from moisture, because the circuit is retained in a non-sealed plastic enclosure.
Fourth, the Horner controller has at least three individual connections which increase the likelihood of improper connections or possible physical damage due to signals being shorted to ground. If the device is not pin for pin compatible with the Horner adapter, a null modem adapter may be required which would increase the individual connections to five. The use of the null modem adapter could also require an even deeper enclosure to be used to contain the programmable controller.
Accordingly, there is a clearly felt need in the art for a voltage conditioning transceiver cable which allows connection to a programmable controller disposed in a tight space, provides monitoring of data transfers, and has the electrical circuitry molded as an integral part of the cable.